Borgert, 1894
— Oozooids with sagittally stretched intestinal tube; oesophagus concavity downwards; the endostyle runs from M2 to M5. Oozooids of Doliolum cannot be separated to species.
— Nurse with M2 to M8 fused in a continuous sheet; body length up to 2 mm. Nurses of Doliolum cannot be separated to species.
— Phorozooids and gonozooids almost identical, though phorozooids have no gonads but bear the buds of the gonozooids on the ventral stalk. The intestine is dextrally arched.
— Trophozooids with numerous gill slits (ca. 10-40), the anal aperture is at the level of the oesophageal funnel. Trophozooids of Doliolum and Dolioletta are still undistinguishable.
The genus Doliolum contains two species, both present in the North Sea: Doliolum denticulatum and Doliolum nationalis. Only as gonozooids these species can be separated.